The pathophysiology of constipation in the setting of longstanding diabetes mellitus is not well understood. We have found that acute hyperglycemia blunts the perception of rectal distention in healthy volunteers without altering rectal compliance or peripheral afferent neural function between the rectum and cortical structures. In the current study, we plan to use PET scanning to localize the forebrain and brainstem structures active during the perception of rectal stimulation. We will further evaluate the effect of acute hyperglycemia on the activation of these structures. The causes of constipation in patients with diabetes mellitus are poorly understood. We have found that elevated blood sugar levels affects the sensation of a balloon inflated in the rectum. We plan to use positron emission tomography to determine which parts of the brain are activated in response to inflating a balloon in the rectum. In addition, we will study whether activation of different parts of the brain is altered after artificially raising a person's blood sugar level.